1. Technical Field
The present invention relates to a semiconductor device capable of transmitting electric signals between two circuits to which the electric signals with different potentials are input.
2. Related Art
When electric signals are transmitted between two circuits to which the electric signals with different potentials are input, photocouplers are generally used. The photocoupler includes a light emitting element, such as a light emitting diode, and a light receiving element, such as a phototransistor. The light emitting element converts an input electric signal into light, and the light receiving element converts the light into the electric signal. In this way, the electric signal is transmitted.
However, since the photocoupler includes the light emitting element and the light receiving element, it is difficult to reduce the size of the photocoupler. When the frequency of the electric signal is high, it is difficult to follow the electric signal. As a technique for solving these problems, for example, U.S. Pat. No. 7,075,329 discloses a structure in which two inductors are formed on the same substrate and the two inductors are inductively coupled to each other to transmit electric signals. In U.S. Pat. No. 7,075,329, when two kinds of electric signals are transmitted, four inductors are formed on the same substrate and two sets of inductors are inductively coupled to each other. Further, in Japanese Published patent application A-H 08-222439 a transformer which is based on square spiral coils formed on semiconductor substrate surface is disclosed. The first coil of the square spiral coils and the second of them have the respective coil patterns almost vertically opposed to catch other with an insulating layer interposed between them and overlapped nearly in the same planer position.
When two kinds of electric signals are transmitted by the inductive coupling between the inductors, two sets of inductors that are inductively coupled to each other are needed. When the distance between two sets of inductors is short, the inductors interfere with each other, and noise is likely to be generated in the electric signal.